The early church recognized the “stamp of divine inspiration” early on. The main attributes that caused these early church leaders to recognize the writings to be divine and, therefore, necessary for inclusion into the canon were apostolicity, orthodoxy, antiquity, and ecclesiastical usage. Apostolicity refers to whether the author was either an apostle himself, or working under the authority of an apostle. Orthodoxy refers to whether a piece of writing was consistent with the theology of scripture that had been previously revealed as divine, including the Old Testament. The attribute of antiquity simply means that the book in question must have been written during the time of the apostles. Finally, ecclesiastical usage speaks about whether early church was already using distributing, teaching, and using the book.
Andreas J. Köstenberger, et. al., The Cradle, the Cross, and the Crown (Nashville: B&H Publishing Group, 2009), 8-10.